Messages in this thread | | | Date | Tue, 24 Jul 2018 18:17:39 +0100 | From | Patrick Bellasi <> | Subject | Re: [PATCH v2 12/12] sched/core: uclamp: use percentage clamp values |
| |
On 24-Jul 10:11, Suren Baghdasaryan wrote: > On Tue, Jul 24, 2018 at 9:43 AM, Patrick Bellasi > <patrick.bellasi@arm.com> wrote: > > On 21-Jul 21:04, Suren Baghdasaryan wrote: > >> On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi > >> <patrick.bellasi@arm.com> wrote: > > > > [...] > > > >> > +static inline unsigned int scale_from_percent(unsigned int pct) > >> > +{ > >> > + WARN_ON(pct > 100); > >> > + > >> > + return ((SCHED_FIXEDPOINT_SCALE * pct) / 100); > >> > +} > >> > + > >> > +static inline unsigned int scale_to_percent(unsigned int value) > >> > +{ > >> > + unsigned int rounding = 0; > >> > + > >> > + WARN_ON(value > SCHED_FIXEDPOINT_SCALE); > >> > + > >> > + /* Compensate rounding errors for: 0, 256, 512, 768, 1024 */ > >> > + if (likely((value & 0xFF) && ~(value & 0x700))) > >> > + rounding = 1; > >> > >> Hmm. I don't think ~(value & 0x700) will ever yield FALSE... What am I missing? > > > > So, 0x700 is the topmost 3 bits sets (111 0000 0000) which different > > configuration corresponds to: > > > > 001 0000 0000 => 256 > > 010 0000 0000 => 512 > > 011 0000 0000 => 768 > > 100 0000 0000 => 1024 > > > > Thus, if 0x700 matches then we have one of these values in input and > > for these cases we have to add a unit to the percentage value. > > > > For the case (value == 0) we translate it into 0% thanks to the check > > on (value & 0xFF) to ensure rounding = 0. > > > > I think just (value & 0xFF) is enough to get you the right behavior. > ~(value & 0x700) is not needed, it's effectively a NoOp which always > yields TRUE. For any *value* (value & 0x700) == 0x...00 and ~(value & > 0x700) == 0x...FF == TRUE.
And you are actually right! ;)
> > Here is a small python snippet I've used to check the conversion of > > all the possible percentage values: > > > > ---8<--- > > values = range(0, 101) > > for pct in xrange(0, 101): > > util = int((1024 * pct) / 100) > > rounding = 1 > > if not ((util & 0xFF) and ~(util & 0x700)):
... it works also by patching the line above!
> > print "Fixing util_to_perc({:3d} => {:4d})".format(pct, util) > > rounding = 0 > > pct2 = (rounding + ((100 * util) / 1024)) > > if pct2 in values: > > values.remove(pct2) > > if pct != pct2: > > print "Convertion failed for: {:3d} => {:4d} => {:3d}".format(pct, util, pct2) > > if values: > > print "ERROR: not all percentage values converted" > > ---8<---
Good catch, thanks!
-- #include <best/regards.h>
Patrick Bellasi
| |